Emulsion aggregation toners are excellent toners to use in forming print and/or xerographic images in that the toners may be made to have uniform sizes and in that the toners are environmentally friendly. U.S. patents describing emulsion aggregation toners include, for example, U.S. Pat. Nos. 5,370,963, 5,418,108, 5,290,654, 5,278,020, 5,308,734, 5,344,738, 5,403,693, 5,364,729, 5,346,797, 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256, 5,501,935, 5,723,253, 5,744,520, 5,763,133, 5,766,818, 5,747,215, 5,827,633, 5,853,944, 5,804,349, 5,840,462, and 5,869,215.
Two main types of emulsion aggregation toners are known. First is an emulsion aggregation process that forms acrylate based, e.g., styrene acrylate, toner particles. See, for example, U.S. Pat. No. 6,120,967, incorporated herein by reference in its entirety, as one example of such a process. Second is an emulsion aggregation process that forms polyester, e.g., sodio sulfonated polyester toner particles. See, for example, U.S. Pat. No. 5,916,725, incorporated herein by reference in its entirety, as one example of such a process.
Emulsion aggregation techniques typically involve the formation of an emulsion latex of the resin particles, which particles have a small size of from, for example, about 5 to about 500 nanometers in diameter, by heating the resin, optionally with solvent if needed, in water, or by making a latex in water using an emulsion polymerization. A colorant dispersion, for example of a pigment dispersed in water, optionally also with additional resin, is separately formed. The colorant dispersion is added to the emulsion latex mixture, and an aggregating agent or complexing agent is then added to form aggregated toner particles. The aggregated toner particles are heated to enable coalescence/fusing, thereby achieving aggregated, fused toner particles.
Fluorescent toners are among the most widely used security printing features. A printed document is usually authenticated by detecting the light emitted by the fluorescent component when subjected to black light. The light emitting property cannot be reproduced in a second generation copy.
Fluorescent dyes used in fluorescent inks and toners may lose fluorescence in the print-head when the ink is heated to a temperature greater than 120° C. to melt during normal operation. To overcome this problem, the security printing industry uses hard, robust pigments containing the dye of interest. Pigments are preferred over fluorescent dyes because of their improved chemical, light fastening and thermal stability. Pigments are also preferred by the industry because there is limited or no migration or bleeding of the dye compound.
Most commercially available fluorescent pigments are made by grinding a bulk polymer matrix containing fluorescent materials. This process does not result in fluorescent particles of a size smaller than 1-2 microns, and typically the size of these particles is about 4-5 microns. According to this process, fluorescent dyes are incorporated into hard, crosslinked particles, thereby limiting the mobility of the fluorescent dye. Once the fluorescent dye is isolated from interaction with other materials present in the ink and, chemical degradation by the environment is diminished. These hard particles are dispersed in the marking material, typically liquid inks.
Inks based on fluorescent pigments are currently used in rotogravure, flexographic, silk-screening and off-set printing systems. However, given their large size, inks based on these pigments cannot be used with inkjet, solid ink or UV curable inks, because they physically clog the ink jet nozzles. In addition, they are unsuitable for fabrication of EA toners since the size of the fluorescent particles is about the size of the toner particles.
Thus, there is a need for fluorescent compositions, including fluorescent compositions that may be used in/with inkjet inks, solid inks, UV curable inks and EA (Emulsion Aggregation) toners and that have suitable thermal degradation properties. There is a further need for fluorescent compositions of such small size that may be used in/with inkjet inks, solid inks, UV curable inks and EA toners and that are compatible with organic based marking materials.
The present disclosure addresses these needs by providing emulsion aggregation toners containing at least one nanoscale fluorescent pigment particle and/or at least one fluorescent organic nanoparticle, and the use of such emulsion aggregation toners in methods for forming images.